In a known manner, an ad hoc network has no fixed infrastructure, and has stations equipped with a radio transmitting and/or receiving means and appropriate protocols form the nodes of the network and communicate with each other using one or more shared radio channels.
Ad hoc networks are in particular used to carry out tactical communications between military teams moving over combat zones. For example, each team has a radio transceiver station that constitutes a node of the network. Several teams are generally grouped together in groups, the teams within a same group for example falling under a same hierarchical commander.
There are two types of communication needs within such an ad hoc network: communications reserved for teams in the same established group and generally pertaining to hierarchical services; these communications are transmitted and received by nodes of the same group and can only pass through nodes in that group; and communications relative to geographical services, which in particular depend on the proximity of the nodes and not the group to which a node belongs. Below, the terms geographical or cross communications or messages refer to those communications or messages that are relayed based solely on geographical proximity, and not membership in a group.
One problem encountered in tactical communications is the low capacity of each radio channel (for example, a VHF radio channel has a width of 25 kHz), which limits the capacity of the ad hoc network and therefore the number of nodes that can be implemented therein, or which limits the services that can be rendered to them.
A first solution to resolve this problem is to increase the width of a channel, for example by increasing it to 75 kHz for a VHF channel, which makes it possible to increase the available throughput for the geographical services.
A second solution to resolve this problem is to use different 25 kHz channels non-simultaneously, for unique communication purposes, i.e., internal, within each group. The number of nodes in each group is limited. Each group has a channel dedicated to it during only a fraction of the radio frame. Different groups can use different 25 kHz channels at the same time, which makes it possible to increase the overall throughput and services rendered. In order to allow shared communication by all groups, a shared gateway channel must be established on another fraction of the frame.
The main drawback of the first solution lies in its shorter range, at an equivalent power, which consequently requires redeveloping new protocol and networking layers to take advantage of the increased bandwidth. This first solution thus does not make it possible to resolve the maintenance of the range and widening of the throughput for cross communications simultaneously.
The main drawback of the second solution lies in the lack of capacity of the gateway channel that is necessary for geographical services based on the geographical proximity of the communicating nodes and which can therefore correspond to communications between nodes in a same group or nodes in different groups. This second solution makes it possible to increase the throughput for group communications, but does not make it possible to increase the throughput for cross communications.
The present invention aims to make it possible to increase the available resources for cross communications.